Apparatus for promoting the vigilance of a vehicle operator using monocular display

ABSTRACT

The present invention is heads up display for use in a ground vehicle. A video program source and a display device produce a set of visual images which are reflected to only one eye of the driver via a mirror disposed on the windshield at a position slightly above the normal line of sight of the driver. This mirror has a size which is a small fraction of the windshield area, a width less than the interpupilary distance, and has a size relative to the size of the display device and the distance from the driver to the display device to reflect an image of the display device to only one eye of the driver. This could be either the left eye or the right eye. The display device is surrounded by a dark unobtrusive background which enables the reflected image other than the display to be visually uninteresting. The mirror has a optical power for reflecting a collimated image focused at visual infinity. A hood is provided for the display to prevent direct ambient light from falling on the display, thus preserving the contrast of the display. The apparatus optionally includes a second mirror which enables the passenger to also view an image of the display device.

TECHNICAL FIELD OF THE INVENTION

The technical field of the present invention is head up displays forvehicles, and in particular head up displays for ground vehicles (suchas automobiles) of the type described in U.S. Pat. No. 4,742,389.

BACKGROUND OF THE INVENTION

My prior U.S. Pat. N. 4,742,389 entitled "Apparatus for Promoting theVigilance of a Motor Vehicle Operator" taught a technique for display ofa video program of moving visual images to the driver of a groundvehicle while operating the ground vehicle. In accordance with theteachings of that patent, the visual display, having a size which is asmall fraction of the total windshield area, is presented on thewindshield of an automobile at a position slightly above the line ofsight of the driver toward the direction of travel of the automobile.This does not interfere with the visual task of operating theautomobile. On the contrary, it has been found that in some occasionsthis display actually enhances the attention of the driver to the visualtask of operating the automobile.

The present invention is an improvement on this prior invention whichenables presentation of the visual image to only a single eye of thedriver. It has been found that the operator of a ground vehicle canstill enjoy the visual program when presented to a single eye. Thispresentation of the image to a single eye of the user enables the mirroremployed to be smaller than would be required to present the image toboth eyes. This results in a smaller area of the windshield beingblocked by the apparatus. In particular, the display is so small that itnever simultaneously blocks the view of both eyes to objects locatedoutside of the vehicle. These aspects of the invention serve to increasethe safety of the apparatus.

SUMMARY OF THE INVENTION

The present invention is an apparatus for use in a ground vehicle havinga windshield through which the driver can see conditions in thedirection of travel of the ground vehicle. This invention includes avideo program source and a display device for producing a set of visualimages. The video program source can be an entertainment source such asa broadcast television receiver, a video tape player or a video discplayer, or it can be related to the operation of the ground vehicle suchas map displays, instrument readings for the ground vehicle or the viewof a camera disposed to cover a blind spot of the driver. In thepreferred embodiment the ground vehicle is an automobile.

A mirror is disposed on the windshield of the automobile at a positionslightly above the normal line of sight of the driver. This mirror has asize which is a small fraction of the windshield area. In addition, thismirror has a width which is less than the interpupillary distance, thedistance between the pupils of the driver's eyes. The size of the mirroris further limited relative to the size of the display device, thedistance from the driver to the mirror, and the distance from the driverto the display device to reflect an image of the whole of the displaydevice to only, a single eye of the driver without reflecting an imageof any part of the display to the other eye. This single viewing eye ofthe driver could be either the right eye or the left eye of the driver.Thus the height and width of the mirror are limited by the geometry ofthe apparatus and in all events must be a small fraction of the totalwindshield area, and the width must be less than the interpupillarydistance.

In a further feature of the present invention, the display device issurrounded by a dark unobtrusive background. This feature has twoadvantages. The mirror is preferably made slightly larger than necessaryto reflect an image of the whole display to the single eye of thedriver. This is preferable in order to reflect an image of the wholedisplay to the single eye while permitting slight movements of the head.It has been found that the likely movements of the driver's head requirea greater excess in width than in height. Otherwise such slightmovements of the head would require adjustment of the mirror. Thus innormal use the mirror will reflect to the eye of the driver an image ofareas surrounding the display. The provision of such a backgroundenables this image of the surrounding area to be of this backgroundonly. In addition, the other eye of the driver, if directed to themirror, will also receive a reflected image of this background. Thisprevents capture of the driver's attention by a reflected image otherthan the display.

In accordance with the preferred embodiment of the present invention,the system presents a collimated image to the single eye of the user,this collimated image focused at or near visual infinity. This causesthe driver to focus the viewing eye at very near the proper focus forviewing developing traffic conditions outside the vehicle. Thus verylittle effort is required for the driver to shift attention from thedisplay to the traffic conditions ahead of the vehicle. The preferredmethod of collimating the image is with a mirror having an opticalpower. The optical power can be achieved through the use of a curvedmirror or the use of a flat holographic optical element having theproper diffraction pattern to achieve the necessary optical power. It isalso feasible to produce a collimated image using one or more lensesbetween the display and the eye of the driver.

In a yet further feature of the present invention, the display device isfitted with a hood directed toward the mirror. This hood reduces theopportunity for any bright ambient light to fall directly on the displaydevice and "wash-out" the contrast of the display. This hood ispreferably slanted toward the mirror along the optical path to the eyeof the driver.

The program source preferably produces an accompanying audio programwhich is made audible by a speaker. Examples of such a source ofcorresponding video and audio programs include a broadcast televisionreceiver, a video tape player and a video disc player.

In a still further aspect of the present invention, a second mirror isdisposed on the windshield on the passenger's side of the vehicle. Thissecond mirror permits the passenger to view the video program. Thissecond mirror may be monocular as in the case of the primary mirror.Alternatively, this second mirror may be of a size greater than theinterpupillary distance enabling the passenger to view the display withboth eyes.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and aspects of the present invention will becomeclear from the following description in conjunction of the drawings inwhich:

FIG. 1 is a schematic drawing of the present invention disposed in anautomobile;

FIG. 2 illustrates a perspective view of a curved mirror which may beemployed in the present invention;

FIG. 3 illustrates a perspective of a mirror formed of compoundholographic optical elements which may be employed in the presentinvention;

FIG. 4 illustrates in block diagram form a broadcast television receiverwhich may form the signal source of the present invention;

FIG. 5 illustrates in block diagram form a video tape player which mayform the signal source of the present invention;

FIG. 6 illustrates in block diagram form a video disc player which mayform the signal source of the present invention;

FIG. 7 is a schematic drawing of the optical paths related to themirrors of the present invention;

FIG. 8 illustrates the use of the primary mirror of the presentinvention to reflect an image of the display device to the left eye ofthe user;

FIG. 9 illustrates the use of the primary mirror of the presentinvention to reflect the image to the right eye of the user; and

FIG. 10 illustrates the use of a background material surrounding theimage display device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates in schematic form the invention disposed in anautomobile. FIG. 1 shows an automobile having a forward body panel 12, arelatively transparent windshield 14 made of glass, plastic, or othersimilar material, and a steering wheel 16. The steering wheel 16 isattached to a steering column 18 which passes forward through a dashpanel 20. Disposed below the windshield 14 is a dash board 32.

The driver's eyes 22 are located at some relatively unchanging positionwith respect to the components of the automobile just mentioned. Theview of driving conditions ahead of the automobile are presented to thedriver's eyes 22 by means of light rays 24, which are shown as cast at aslight downward angle toward the pavement upon which the automobile istraveling. The light rays 24 composing the scene ahead of the automobilepass through windshield 14 virtually undistorted.

A video program source 40 produces a video program and optionally anaccompanying audio program. The video program is coupled to displaydevice 50 via a cable 42. Display device 50 is preferably a colorcathode ray tube. The audio program is coupled to speaker 44 via a cable46. Those skilled in the art would recognize that speaker 44 need not bedisposed in the ceiling of the vehicle. Speaker 44 can be disposed inany location within the passenger cabin of the vehicle likely to permitthe passengers to hear its sound output.

A diverging wave front of rays 56 of display device 50 is directedtoward a mirror 54, which is mounted via mirror mount unit 58 onto aportion of windshield 14. In accordance with the teachings of U.S. Pat.No. 4,742,389, mirror mount unit 58 is disposed so that mirror 54 islocated slightly above the line of sight of the driver toward thedirection of travel of the automobile. In addition, mirror 54 is sosized as to utilize no more than a small fraction of the totalwindshield area. In accordance with the present invention, the width ofmirror 54 is less than the distance between the pupils of the driver'seyes, the interpupillary distance. In addition, mirror 54 must have aheight and width with relation to the distance from the driver's eye 22to mirror 54, the distance from mirror 54 to the display device 50, andthe size of display device 50 so that an image of display device 50 ispresented to only one eye. As an example, a rectangular mirror 54 havingdimensions of approximately 2.5 inches wide by 1.6 inches high has beenfound suitable for use with a mid-sized automobile based upon thedistance from the windshield 14 to the driver's eyes 22. FIG. 1 furtherillustrates hood 52, whose character and purpose will be furtherexplained below.

In accordance with the preferred embodiment of the present invention,mirror 54 has optical power in order to present an image to the driver'seyes 22 via rays 34 which appears focused near visual infinity or atvisual infinity. The provision of an image near or at visual infinitypermits the driver to shift his attention from the mirror 54 to the viewof traffic conditions ahead of the vehicle without a great change in thefocus of his eyes. This enhances the safety of the apparatus of thisinvention.

There are two techniques contemplated for providing this optical power.The optical power can be achieved through the use of a curved reflectingmirror. In this case the curvature must be selected to provide thedesired image to the driver's eye as illustrated in FIG. 2.Alternatively, the optical power can be achieved through the use of aflat holographic optical element. In this case the holographic opticalelement must have the proper diffraction pattern to achieve thenecessary optical power. Such holographic optical elements are wavelength dependent. However, the phosphors used in the color cathode raytube have known colors. Therefore a compound holographic optical elementcan be constructed having the same optical power for each phosphor colorsuch as the three holographic optical elements 54R, 54G and 54Billustrated in FIG. 3.

A collimated image may be produced without using a mirror having opticalpower. One or more lenses may be employed in the optical path, eitherbetween the display and the mirror or between the mirror and the eye ofthe user, or both. The essential point is that the rays reaching thedriver's eye form a virtual image which appears focussed at somedistance approximating visual infinity.

In accordance with the present invention, signal source 40 couldconstitute an entertainment source or a source related to the operationof the ground vehicle. Examples of entertainment sources include: abroadcast television receiver capable of receiving a broadcasttelevision program including antenna 102, television tuner 104, videoamplifier 106 and audio amplifier 108 as illustrated in FIG. 4; a videotape player including video tape playback deck 114, video amplifier 116and audio amplifier 118 as illustrated in FIG. 5; a video disc playerincluding video disc playback deck 124, video amplifier 126 and audioamplifier 128 as illustrated in FIG. 6; each similarly capable ofproducing a combined video and audio program. Examples of sourcesrelated to the operation of the ground vehicle include map displayscorresponding to the intended travel path of the ground vehicle, andvarious instrument readings concerning the operation of the groundvehicle. Signal source 40 may also include the views of one or moretelevision cameras, such as a camera disposed to view conditions behindthe ground vehicle or a camera disposed to cover a blind spot of thedriver of the ground vehicle. The essential point is that signal source40 generate at least a video signal which can be viewed by the drivervia the reflected image appearing in mirror 54.

FIG. 7 illustrates the optical system schematically. Right eye 22R andleft eye 22L of the driver are disposed at a relatively unchangingdistance from windshield 14. FIG. 7 illustrates the mirror 54 adjustedto reflect an image of the display device 50 via rays 56 and rays 34 toonly right eye 22R. Mirror 54 is of such a size that it reflects animage of background 90 via rays 74 and rays 72 to left eye 22L.

Display device 50 is shown laterally displaced from the position of thedriver. The driver is typically seated in the left portion of the frontseat of the vehicle. It has been found that there is typically morespace to accommodate the display device 50 in the central portion of thevehicle ceiling. Placing display device 50 at this location requiresmirror 54 to be slightly turned to properly reflect the image of displaydevice 50 to the eye 22R of the driver. It is also contemplated that thelocation of display device 50 will be slightly higher than the locationof the eye 22 of the driver, requiring a slight upward tilt in mirror54. The essential point is that mirror 54 is disposed slightly above theview of the driver to traffic conditions ahead of the vehicle and isoriented to reflect an image of display device 50.

In accordance with the present invention, mirror 54 has a size relativeto the optics of the system to prevent reflection of an image of displaydevice 50 to left eye 22L. As illustrated in FIG. 7, if the driver wereto view mirror 54 with left eye 22L, the driver would see an image ofthe background 90 surrounding the display device 50 via rays 74 and 72.The driver could only see an image of display device 50 in mirror 54 ifthe mirror were extended to the left.

The particular size of mirror 54 needed to reflect an image of all ofdisplay device 50 to right eye 22R without reflecting an image of any ofdisplay device 50 to left eye 22L depends on the particular geometry ofthe installation. Features in the geometry effecting this size includethe total optical path distance from the eyes of the driver to displaydevice 50, the distance from mirror 54 to the eyes of the driver, andthe size of display device 50. This invention relies on the fact thatthe two eyes of the driver have different viewing paths to the displaydevice 50 (parallax). Complete separation of these optical paths sets amaximum size of display device 50 relative to the geometry of theapparatus.

FIG. 7 illustrates another advantageous feature of constructing mirror54 having a width less than the interpupillary distance. Projected rays34' define the cone of view of right eye 22R blocked by mirror 54.Likewise, projected rays 72' define the cone of view of left eye 22Lblocked by mirror 54. Because mirror 54 has a width less than theinterpupillary distance between left eye 22L and right eye 22R, there isa distance 80 beyond which these obstructed view cones no longercoincide. This means for an object located further from windshield 14than distance 80, mirror 54 cannot simultaneously block the view of botheyes to the object. By proper selection of the width of mirror 54, thisdistance 80 can be made on the order of a car length. Objects closer tothe vehicle than such a distance would likely have an angular extentpreventing complete blockage by mirror 54, even if some parts would becompletely blocked to both eyes. Objects located further than thisdistance will always be visible in at least one eye. Thus the driver'sview of conditions outside the vehicle is less obstructed by a mirrorhaving a width in accordance with the present invention.

The most likely objects to be blocked by mirror 54 are traffic signalsor overhead road signs. These are the most likely to be blocked becausemirror 54 is disposed slightly above the normal line of sight towarddeveloping traffic conditions. Overhead road signs will generally not bea problem to view because they are typically viewed while the vehicle ismoving. Thus such signs will normally not remain at the angle blocked bymirror 54 for long. Traffic signals are often viewed while stopped andthus may remain at a position obscured by mirror 54 for some time. Thusthe size of mirror 54 of the present invention insures that trafficsignals will always be visible to at least one eye. A typical driverwill find that either his attention will be directed to the eye whichcannot view the projected image enabling the traffic signal to be seen,or that he will see the traffic signal superimposed over the projectedimage. In either case the driver will be able to see the traffic signal.

FIG. 7 illustrates a further feature of the present invention. A mirror55 is disposed on the windshield 14 in front of the eyes 23L and 23R ofa passenger in the vehicle. Mirror 55 may be mounted in the sameposition relative to the head of the passenger 23 as mirror 54 is inrelation to driver 22, that is, slightly above the normal line of sighttoward developing traffic conditions. This position is not required formirror 55 as is the case for mirror 54, because the passenger'sattention to the road is less critical to the operation of the vehicle.Mirror 55 could be constructed of the same size as mirror 54, thuspermitting the passenger to view an image of display device 50 with onlya single eye. It is also possible to construct mirror 55 larger than theinterpupillary distance in a manner permitting the passenger to viewdisplay device 50 with both eyes. As illustrated in FIG. 2, thepassenger may view display device 50 via left eye 23L along rays 73 and75 and via the right eye 23R along rays 77 and 79. This requires alarger mirror because the image to the eyes 23L and 23R are reflected byseparate sections of mirror 55. A larger mirror in this location is notobjectionable because the passenger's view of the traffic conditionsoutside the vehicle is not critical to the safe operation of thevehicle.

It is preferable to provide a collimated image to the passenger. Thiscan be achieved in any manner previously discussed for presenting acollimated image to the driver. The presentation of such a collimatedimage is not as critical for the passenger as for the driver, because itis less critical that the passenger be able to quickly change attentionfrom the image to conditions outside the vehicle. Thus this feature neednot be implemented in the present invention.

FIG. 7 further illustrates hood 52. Hood 52 is disposed in front ofdisplay device 50. Hood 52 serves to reduce the chance of ambient lightfalling directly on display device 50. Such direct ambient light wouldundesirably reduce the contrast of the display to the driver. Note thathood 52 is slanted to accommodate the optical path from display device50 to mirror 54. This slant is dependent upon the lateral displacementof display device 50 and the total optical path distance from the driverto display device 50. FIG. 7 illustrates in dashed lines theconstruction of an alternative hood 52'. This alternative constructionis employed when the apparatus includes mirror 55 to enable thepassenger to view display device 50.

FIGS. 8 and 9 illustrate the alternative results of the proper sizing ofmirror 54. FIG. 8 illustrates the presentation of image 60 of thedisplay device 50 via mirror 54 to the left eye of the user. Althoughthe optical power of mirror 54 can present an image focused near or atvisual infinity to the eye of the driver, it cannot compensate for theparallax due to the different position of the two eyes of the driver.The image of the display device 50 to the right eye would have appearedat image 70 in FIG. 8, however mirror 54 is so sized as to not reflectthis image 70 of display device 50 to the right eye of the driver.Therefore, the mirror 54 displays this image to only the left eye of theuser.

FIG. 8 further illustrates that mirror 54 is slightly larger in sizethan needed to reflect an image 60 of display device 50. This excesssize results in reflection of an image 62 of portions of background 90surrounding display device 50. This excess in the size of mirror 54 overthat necessary to produce an image 60 of the whole display device 50permits the apparatus to accommodate slight movements of the driver'shead and eyes without requiring change in the angle of mirror 54. Notethat there is a greater excess size of mirror 54 in the horizontaldimension than in the vertical dimension. This is because it is expectedthat the driver will make horizontal movements of his eye to a greaterdegree than vertical movements. By this means, the driver can change theposition of his head relative to mirror 54 to a small degree withoutneeding to adjust mirror 54 to view display device 50.

Similarly, FIG. 9 illustrates reflection via mirror 54 of image 60 ofdisplay device 50 to the right eye of the driver. In a manner similar tothat described above in conjunction with FIG. 8, the image of displaydevice 50 would have appeared at image 70 with respect to the left eyeof the driver. However, because the mirror 54 does not exist at thisposition, this image 70 is not reflected to the left eye of the driver.FIG. 9 also illustrates reflection of an image 62 of background 90surrounding the image 60 of display device 50.

Selection of the eye of the driver which receives the reflected image 60of display device 50 is dependent upon the horizontal angle of mirror54. A slight change in this angle can change from the situationillustrated in FIG. 3 to the situation illustrated in FIG. 9, or viceversa. Some drivers will find it more comfortable to set mirror 54 forreflection of the image to their left eye. Other drivers will find thatit is preferable to view the image with their right eye. This selectionwould ordinarily be dependent upon which is the dominant eye, the eyewhich is favored in the brain's image formation. The present inventionenables the selected eye to be readily changed by a slight adjustment inthe angle of mirror 54.

FIG. 10 illustrates the provision of a background 90 surrounding thedisplay device 50. Background 90 is preferably of some dark,unornamented material having no visual features. As explained above inconjunction with FIGS. 3 and 4, mirror 54 is slightly larger thannecessary to reflect an image of display device 50, resulting inreflection of an image 62 surrounding display 54. In addition mirror 54is sized so as to reflect an image of display device 50 to only a singleeye of the user. However, the mirror 54 does reflect an image ofsomething to the opposite eye of the user. In the case of the structureillustrated in FIG. 10, the reflected image 62 surrounding the image 60and this "something" reflected to the other eye is the background 90.This background 90 is preferably dark and visually uninteresting.Therefore, the attention of the driver is not captured by any reflectionfrom mirror 54 other than display device 50 and the driver cansuccessfully ignore any such reflection. Without such a background, itmay in some situations be possible for the reflection of an imageincluding objects outside the vehicle if, for example, the displaydevice 50 were located relatively far back in the ceiling of thevehicle. In such an event, the driver's attention is liable to becaptured by objects outside the vehicle which are reflected via mirror54. This disadvantage is eliminated by the use of the background 90.

I claim:
 1. An apparatus for use in a ground vehicle having a windshieldthrough which the driver can view conditions in the direction of travelof the ground vehicle, the apparatus comprising:a program source forproducing a video program; a display device connected to said programsource for producing a set of visual images corresponding to said videoprogram; and a mirror disposed in a location slightly above the normalline of sight of the driver toward the direction of travel of the groundvehicle, said mirror having a width which is less than theinterpupillary distance between the driver's eyes, said mirror having awidth and a height in relation to the size of said display device andthe distance from the driver to said mirror to reflect an image of theentirety of said display device to one eye of the driver and not toreflect an image of any of said display device to the other eye of thedriver.
 2. The apparatus claimed in claim 1, wherein:said mirror havingan orientation such as to reflect said image of the entirety of saiddisplay device to only the left eye of the driver.
 3. The apparatusclaimed in claim 1, wherein:said mirror having an orientation such as toreflect said image of the entirety of said display device to only theright eye of the driver.
 4. The apparatus claimed in claim 1,wherein:said mirror is disposed on the windshield of the ground vehicle.5. The apparatus claimed in claim 1, further comprising:a dark, visuallyuninteresting background surrounding said display device.
 6. Theapparatus claimed in claim 1, further comprising:an optical systemdisposed in the optical path between said display device and the eye ofthe driver for providing a collimated image of said display device tothe eye of the driver.
 7. The apparatus claimed in claim 6, wherein:saidoptical system includes at least one lens.
 8. The apparatus claimed inclaim 1, wherein:said mirror has an optical power for reflecting acollimated image of said display device to the eye of the driver.
 9. Theapparatus claimed in claim 8, wherein:said mirror has a curvedreflecting surface for achieving said optical power.
 10. The apparatusclaimed in claim 8, wherein:said mirror includes at least oneholographic optical element having a diffraction pattern therein forachieving said optical power.
 11. The apparatus claimed in claim 1,further comprising:a hood disposed on said display device for reducingthe possibility of ambient light falling directly on said displaydevice.
 12. The apparatus claimed in claim 1, further comprising:anaudio program source for producing an audio program corresponding tosaid video program; and a speaker connected to said audio program sourceand disposed within the ground vehicle for audibly reproducing saidaudio program.
 13. The apparatus claimed in claim 12, wherein:said videoprogram source and said audio program source consist of a broadcasttelevision receiver.
 14. The apparatus claimed in claim 12, wherein:saidvideo program source and said audio program source consist of a videotape player.
 15. The apparatus claimed in claim 12, wherein:said videoprogram source and said audio program source consist of a video discplayer.
 16. The apparatus claimed in claim 1, further comprising:asecond mirror disposed in a location on the passenger's side of theground vehicle, said mirror having a size and location to reflect animage of said display device to at least one eye of a passenger.
 17. Theapparatus claimed in claim 16, wherein:said second mirror is disposed onthe windshield of the ground vehicle.
 18. The apparatus claimed in claim16, wherein:said second mirror is disposed in a location slightly abovethe normal line of sight of the passenger toward the direction of travelof the ground vehicle.
 19. The apparatus claimed in claim 16,wherein:said second mirror has a width which is less than theinterpupillary distance between the passenger's eyes, said mirror havinga width and a height in relation to the size of said display device andthe distance from the passenger to said mirror to reflect an image ofthe entirety of said display device to only one eye of the passenger andnot to reflect an image of any of said display device to the other eyeof the passenger.
 20. The apparatus claimed in claim 16, wherein:saidsecond mirror has a width which is greater than the interpupillarydistance between the passenger's eyes, said mirror having a width and aheight in relation to the size of said display device and the distancefrom the passenger to said mirror to reflect an image of the entirety ofsaid display device to each eye of the passenger.
 21. An apparatus foruse in an ground vehicle having a windshield through which the drivercan view conditions in the direction of travel of the ground vehicle,the apparatus comprising:a display means for producing a visual imagecorresponding to a video program disposed in a location slightly abovethe normal line of sight of the driver toward the direction of travel ofthe ground vehicle, said display means having a width which is less thanthe interpupillary distance between the driver's eyes.
 22. The apparatusclaimed in claim 21, further comprising:an optical system disposed forproviding a collimated visual image of said video program to the eye ofthe driver.
 23. The apparatus claimed in claim 21, further comprising:anaudio program source for producing an audio program corresponding tosaid video program; and a speaker connected to said audio program sourceand disposed within the ground vehicle for audibly reproducing saidaudio program.
 24. The apparatus claimed in claim 21, wherein:saiddisplay means produces said visual image in a fashion visible to only asingle eye of the driver.
 25. An apparatus for use in a ground vehiclehaving a windshield through which the driver can view conditions in thedirection of travel of the ground vehicle, the apparatus comprising:aprogram source for producing a video program; a display device connectedto said program source for producing a set of visual imagescorresponding to said video program; and a mirror disposed in a locationon the windshield, said mirror having a width which is less than theinterpupillary distance between the driver's eyes, said mirror having awidth and a height in relation to the size of said display device andthe distance from the driver to said mirror to reflect an image of theentirety of said display device to one eye of the driver and not toreflect an image of any of said display device to the other eye of thedriver.
 26. An apparatus for use in a ground vehicle having a windshieldthrough which the driver can view conditions in the direction of travelof the ground vehicle, the apparatus comprising:a display means forproducing a visual image corresponding to a video program disposed in alocation on the windshield, said display means having a width which isless than the interpupillary distance between the driver's eyes.